pasdivert

Pascal binding for WinDivert.

This Unit can be used with Delphi and Free Pascal.

WinDivert

Copied from the Website: WinDivert is a user-mode packet capture-and-divert package for Windows Vista, Windows 2008, Windows 7, Windows 8 and Windows 10.

WinDivert allows user-mode applications to capture/modify/drop network packets sent to/from the Windows network stack.

WinDivert can be used to implement user-mode packet filters, packet sniffers, firewalls, NAT, VPNs, tunneling applications, etc.

GitHub repository of WinDivert: https://github.com/basil00/Divert

Requirements

You need the binary distribution from the WinDivert homepage. Since we use it with Pascal/Delphi you can use any distribution (VS, DDK or MinGW), this does not matter because we do not need the lib files for linking.

On Windows 64 put win64\WinDivert64.sys and win64\WinDivert.dll in the program directory.

On Windows 32 put win32\WinDivert32.sys and win32\WinDivert.dll in the program directory.

Examples

Please run these examples as Administrator. To debug them with Delphi run Delphi as Administrator.

• passthru This program does nothing except divert packets and re-inject them.
• netdump This is a simple traffic monitor. It uses a WinDivert handle in SNIFF mode. The SNIFF mode copies packets and does not block the original.
• webfilter This is a simple web (HTTP) filter using WinDivert.
• netlimit Simulates bad networks.
• dnsdump This is a simple DNS traffic monitor.

webfilter

Is a simple web (HTTP) filter using WinDivert.

It works by intercepting outbound HTTP GET/POST requests and matching the URL against a blacklist. If the URL is matched, we hijack the TCP connection, reseting the connection at the server end, and sending a blockpage to the browser.

Example

webfilter blacklist.txt [blacklist2.txt ...]

This blacklist.txt will block all HTTP requests to example.com, Google and Facebook domains.

example.com
google.com
facebook.com

netlimit

A Program to simulate bad networks. Can add latency and drop packets.

This program can be useful when you have to test client/server programs (such as online games) which must be able to deal with bad/unreliable networks (e.g. the Internet). For example, you can't test lag compensation, server/client prediction when you have an almost perfect network (localhost, LAN).

Example

netlimit -f "outbound and udp.DstPort == 3337" -t 1 -l 1000 -d 20

1. Filter outbound UDP traffic on port 3337
2. Use 1 worker thread
3. Simulate an average ping of ~1000 ms (between 500 ms and 1500 ms)
4. Drop 20 % packets

Compiling

To compile the examples on Windows 64 with Free Pascal, download the latest 32-Bit Lazarus distribution (at the moment of this writing, it's Lazarus 1.4.2 and FPC 2.6.4) and the cross-x86_64-win64-win32 crosscompile add on and install both. Open the project file (*.lpi), select the configuration (Win64-Debug, Win64-Release, Win32-Debug or Win32-Release) and click Start -> Compile.